Coal may be gasified by contacting it with steam and an oxygen containing gas at a temperature generally in the range of about 700.degree. to 1100.degree.C. Products of the gasification reaction include hydrogen, carbon monoxide, carbon dioxide, sulfur compounds such as hydrogen sulfide and carbonyl sulfide and hydrocarbons such as methane. Depending upon gasification conditions, the residue remaining from the gasification reaction may be either an ash or a char. An example of a gasification process which produces a dry ash residue is the Lurgi process while gasification techniques such as the Bureau of Mines-developed Synthane process produce a dry char residue. This char residue may be burned as a fuel in a power plant as a substitute for coal. Such char residues typically contain considerably less sulfur than was contained in the coal which was gasified. However, the coal chars produced during gasification from high sulfur coals retain levels of sulfur above 1.0% and, therefore, do not meet the Environmental Protection Agency's requirements for low sulfur fuels.
It is known to gasify coal in the presence of such materials as lime and dolomite. One example of such a technique is the so-called carbon dioxide acceptor process in which calcined dolomite and char are reacted with steam to produce a methane containing gas and a residue of dolomite and char. This residue of spent dolomite and unreacted char is then introduced into a second vessel where the unreacted carbon is burned with air and the heat produced calcines and regenerates the dolomite. This process is described in U.S. Pat. No. 3,115,394.
It is also known to remove sulfur oxides from flue gases produced by the combustion of coal by contacting those gases with limestone based materials. Finely divided limestone may be injected directly into a boiler furnace at a point somewhat removed from the flame, or particulate limestone or dolomite may be used as a fixed, moving, or fluidized bed to contact and absorb sulfur oxides contained in a flue gas stream. It is also known that combustion of sulfur-bearing coal or oil may be conducted in a fluidized bed of limestone which reacts with sulfur oxides produced during the combustion.